I have struggled with this a lot, actually. It's very difficult if your job is so stressful while you're in the environment, sometimes it transfers to your home environment, with people calling or texting you, or just the events of the day resonating. I think the fact that we DON'T want to deal with it, makes it more stressful. Here's what I've started doing, and it takes a lot of practice too.
1. I take a little bit of time to reflect on what happened throughout the work day. A set amount of time to identify the peaks and pitfalls of the day.
2. I give thanks for the day's high points, out loud or silently in my mind, or I will even write them down.
3. Once I get home, or get to school, I take a little bit of time before starting my next task, to do something calming or something that makes me feel good. If I'm at home, I'll take an hour or so. If I'm at school, of course it will be a little less time because I have to go to class.
4. Sometimes I'll even say to myself when I get to the door, that the problems of the day can't follow me inside. It sounds silly, but sometimes that's what it takes in order to train your mind.
5. If it's not a busy school night, I'll take a few deep breaths, calm myself, and go to the gym and work out as hard as I possibly can, maybe push my limits a bit. This really helps me get my frustrations out.
During the day, I'll think about what I get to do once I leave, and make it something to look forward to, even if it's continuing my netflix marathon.
I still have my days when it's crazy hard to let go of my work stress, but in my case, I have had worse jobs. So when all else fails, I'll say to myself that at least I'm not in the place I was in before.